You might need to get a new roommate:
If the facebook pokes you received during the summer turn into real pokes.
If the only other person you see in the room is Sam Adams
If you get noise complaints from people having a party next door
If the custodial staff won't even go in to clean your bathroom
If words like "Dude" and "Brosef" are used not just in passing conversation but on his or her essays
If he or she wants to be a psychology major and supposedly wants to "help people." This is a sure sign of crazy
If he or she wants to be a business major and supposedly wants to "make lots of money." You will be used more than the toilet after a hard night of partying.
If he or she wants to be a kinesiology major and supposedly wants to "help athletes." This is a sure sign of not only an idiot but a really bad jock who even failed to make the walk-on sewing team. Expect bitter drunken ramblings and internal discord.
If he declares himself a part-time student and a full-time partygoer
If they own a book on "how to succeed in college." This is a good indicator of someone who is such a big sucker and retard that they bought a book that told them how to read the textbook and take the test.
If they comment on your facebook status while they are in the room
If their facebook profile picture has a picture of them with their significant other from high school. Expect massive feuds over the phone and long-distance trips for makeup sex.
If they have more than two condoms in their drawer. Expect either a massive amount of sex, or very VERY lonely ruminative masturbation.
If they ask you how often you will be leaving town or the room.
If they ever watch Dr. Phil
If they ask you to identify the source of any stain on their bed, or even worse: their underpants
If they say you might need earplugs on occasion
If they look too much like the opposite sex and you have a significant other that wants to make surprise visits to your room
If they use acronyms like "LOL" and "OMG" in daily conversation
If they try to introduce their friend to you and it turns out he is imaginary.